Article of manufacture and process of making it

ABSTRACT

Oxygen-bearing copper alloys containing small amounts of tin have been found to provide an alloy of unexpectedly high softening temperatures. With these alloys it is not necessary to deoxidize the copper beyond a nominal oxygen content in the preparation of the high softening temperature oxygen-bearing copper alloys.

United States Patent Servi 1 Mar. 14, 1972 [54] ARTICLE OF MANUFACTURE AND PROCESS OF MAKING IT [72] Inventor: Italo S. Servi, 3 Angler Road, Lexington,

Mass. 02173 [22] Filed: Mar. 6, 1969 [21] Appl.No.: 835,828

Related US. Application Data [63] Continuation-impart of Ser. No. 511,494, Dec. 3,

1965, abandoned.

[52] US. Cl ..75/l54,75/153, 148/32 [51] Int. Cl..... [58] Field of Search [56] References Cited OTHER PUBLICATIONS Trans. of AIME, Vol. 152, 1943, pgs. 103- 105 (Chem. Lib.).

Arsenical and Argentiferous Copper, Gregg, Chemical Catalog Co., NY. 1934 pages 73- 77, 84- 89, 106- (Sci. Lib. TN780/G83).

CDA Symposium, Oct. 10th 1962, London, England, pg. 22. Smart et al., The Metal Industry, Sept. 3, 1943, pg. 153, Sept. 10, l943,pgs. -172.

Pilling et al., Trans. AIME, Vol. 73, 1926, pages 679- 692, (Chem. Lib.).

Primary Examiner-Charles N. Lovell Attorney-Frank E. Robbins and Lowell H. McCaner ABSTRACT Oxygen-bearing copper alloys containing small amounts of tin have been found to provide an alloy of unexpectedly high softening temperatures. With these alloys it is not necessary to deoxidize the copper beyond a nominal oxygen content in the preparation of the high softening temperature oxygen-bearing copper alloys.

3 Claims, 2 Drawing Figures o l l oxyseal coursur 1 80417 30 PPM a ma 20a ARTICLE OF MANUFACTURE AND PROCESS OF MAKING IT CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 51 1,494 filed Dec. 3, 1965 entitled Article of Manufacture and Process of Making It, now abandoned in favor of the instant continuation-in-part application.

FIELD OF INVENTION This invention relates to oxygen-bearing copper materials. More particularly this invention relates to modified oxygenbearing copper alloys that have high-softening temperatures.

In the manufacture of automobile radiator stock, for example, it is desirable to employ materials that have good thermal conductivity and that have high-softening temperatures. There are several known ways for raising the softening temperature of oxygen-bearing copper. One way is by the addition of silver. Unfortunately, expensive amounts of silver must be employed to have commercially significant effects in raising the softening temperatures. This adds substantially to the cost of alloy materials produced in this way. PRIOR ART It is known in the literature that tin has an effect on the softening temperatures of very high-purity copper. For example see Smart et al., The Metal Industry, Sept. 3, 1943, page 153 and Sept. 10, 1943, pages l70-l72. Smart et al., examines the softening temperatures as a function of several impurities added to very high-purity copper. Smart et al., concluded that tin was the more effective element in raising the softening temperature. They go on to state that the presence of oxygen precipitates SnO which is wholly ineffective in raising the softening temperature. Thus it is seen that Smart et al., believed that the presence of oxygen in copper-tin alloys completely nullified the desirable changes that tin can cause in the properties of copper because of the precipitation of SnO Pilling et al., AIME Transactions, Vol. 73, 1926, pages 679-692 discusses the effect of tin with oxygen on the conductivity and ductility of copper. In their article Pilling et al., disclosed an oxygen-bearing copper alloy composition having a lowoxygen content of 0.028 percent and a high-oxygen content of 0.35 percent and a low-tin content of 0.008 percent and a high-tin content of 0.133 percent. There is no pertinent disclosure in Pilling et al., concerning the softening temperalures of their oxygen-bearing copper-tin alloys.

The softening behavior of the Pilling et al. alloys may be estimated by observing that all of the Pilling et al., alloys were annealed in nitrogen for l hour at 400 C. prior to tensile testing (see page 681, lines 4 through 7 from the top of the page) and that high elongations (over 20 percent) and relatively modest tensile strength (34,000 to 37,000 lbs. per square inch) were observed after this heat-treatment (Pilling et al., Table I). This shows that all of the Pilling et al., alloys were well softened after exposure to 400 C. and therefore could not have higher softening temperatures than 400 C. Pilling et al., were not concerned with the softening temperatures but were concerned with the toleration of lead and tin with respect to the two main properties which are essential for electrical applications, namely, ductility and electrical conductivity. Although the tin and oxygen contents at the low end of the claimed range of applicant's alloys overlap the upper end of the tin and oxygen content ranges of the Pilling et al., alloys, the unobviousness of the higher softening temperature alloys as claimed herein will be clearly pointed out.

OBJECTS AND SUMMARY One object of the present invention is to provide new, practical, oxygen-bearing copper alloys that have desirable characteristics for a number of important applications such as, for example, the production ofautomobile radiator stock.

Another object of the invention is to provide oxygen-bearing materials having high-softening temperatures. Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims.

In its broadest aspect this invention comprises an oxygenbearing copper alloy to which has been added an amount of tin sufficient to raise the softening temperature to at least 350 C. and preferably to at least 400 C. In a somewhat narrower aspect the invention includes a high-softening temperature oxygen-bearing alloy containing from about 0.1% to about 0.5% tin. Other aspects of the invention are further described below.

In the drawings:

FIG. 1 is a graphical comparison of the behavior of two oxygen-bearing copper materials upon annealing, one of the materials having a small amount of tin added thereto, and the other being without any added tin, the materials otherwise being substantially identical, and

FIG. 2 is a graphical representation of the effect of different small additions of tin upon an oxygen-bearing copper material, with respect to the softening temperature and with respect to electrical conductivity.

DESCRIPTION OF THE INVENTION The present invention is concerned with oxygen-bearing copper materials of which the oxygen content is in the range from about p.p.m. up to about 600 p.p.m., which is a range equivalent to from about 0.01% up to about 0.06%. The addition of very small amounts of tin to such materials has a marked effect upon the softening temperature, as will presently be demonstrated. The nominal amounts of tin, that are within the scope of the present invention, and that produce the desired effect, are in the range from about 0.1% to about 0.5%. A small, more preferred nominal tin range is from about 0.2% to about 0.4%. Analyzed tin contents of these oxygen-bearing copper alloys range from about 0.08% up to about 0.45%. The free tin content of these alloys ranged from about 0.06% up to about 0.40%with the balance of the tin present as tin oxide.

When tin is added to an oxygen-bearing copper it would be expected that a stoichiometric quantity of tin would react with the oxygen to form tin oxide. However, as the analytical data presented herein specifically will point out, only a portion of the tin is actually present in the alloy as tin oxide. All the alloys of this invention contain a nominal tin content from about 0.1% to about 0.5% and all contain some free tin in solution even at the lowest nominal tin content.

One important practical advantage of the present invention is that the softening temperature of an oxygen-bearing copper material may be raised by the addition of a small amount of tin, without the need for first deoxidizing the copper.

Although the literature references cited above contain references to oxygen-bearing copper alloy materials, the physical properties of the oxygen-bearing copper alloys of the present invention when considered in light of the literature references indicate a difference of kind rather than a difference of degree. For example, it would be necessary in view of the Smart et al., reference to expect that it would be required to add a stoichiometric amount of tin to tie up all the oxygen before there was any effect on the softening temperature. If this reasoning were correct the tin would have no effect on the softening temperature in an alloy containing 0.04% oxygen until the tin content was at least 0.148 percent; i.e., 0.04Xll8.7/32=0.148%; 118.7/32 being the ratio of tin/oxygen in the compound SnO Beyond 0.148% tin the effect would be expected to be felt rather abruptly, i.e., as a linear change, since Smart et al., teaches that even as little as 0.01% tin has a very marked effect on the softening temperature of copper in the absence of oxygen. However a review of the data and the examples of this application show that there is some effect at a nominal tin content as low as 0.06 percent and that there is a significant softening effect at a tin content of 0.1 percent. For example in alloy No. 4 (0.10%Sn, 0.04%O only 48.7 percent of the tin present in the alloy is combined with oxygen in the alloy. ln alloy No. II (0.15%Sn, 0.04% 0 only 49.1 percent of the tin present in the alloy is combined with the oxygen in the alloy. See Table 11. Therefore it is clear that the present invention could not be anticipated from the Smart et al., or Pilling et al. literature references.

To demonstrate the invention, the following procedure was adopted. Several different alloy materials were prepared. The compositions of the alloy materials were carefully controlled. As a control, an oxygen-bearing copper was employed with no tin addition. Then, several tin additions were made to the material, in differing amounts, and the oxygen content was adjusted over a range at two selected levels of tin addition. These different alloy materials were each then processed in the following manner.

Each alloy material was cast in the form of a rod having a diameter of about 0.5 inches and then allowed to air-cool outside the furnace. Each rod was then cold swaged to reduce i diameter about 30 percent. The reduced rod was then annealed for 1 hour at 600 C. (first anneal"). The annealed rod was then cold swaged to effect an additional reduction in diameter of about 16.5 percent, and in some cases, a reduction in diameter of about 88 percent, then annealed again. In this second annealing step, portions of the rod were annealed at various temperatures, which will be identified presently, by referring to them as the temperatures in the second annealing step. The hardness of each rod portion was then determined, in order to evaluate the effectiveness of the tin addition.

The observed data are summarized in Table l below.

The hardness data from Table I were plotted against the annealing temperature, in the manner indicated, in FIG. 1. Other observed hardness data, not included in Table I for brevity, were also used in preparing FIG. 1. For clarity, in FIG. I, only two curves were plotted, one representing a control, alloy No. l, to which no tin has been added, and the other representing a tin addition level of 0.2 percent, alloy No. 15.

There are many ways of defining softening temperature. For present purposes the softening temperature is defined as the annealing temperature at which the curves of FIG. 1 intersect with the horizontal line indicating a hardness of 50. At this hardness level, the curves of all of the alloys fall very steeply, and therefore, the softening temperatures, as presently defined, can be determined with great accuracy.

The softening temperature data, determined in the manner just indicated, were plotted in FIG. 2 against the nominal tin content. As FIG. 2 demonstrates, the effect of the tin addition can be observed when even minute amounts of tin are added, and the effect is striking over a narrow range, after which the use of increased amounts of tin is not accompanied by a proportional increase in effect. A preferred addition range, as indicated by FIG. 2, is from about 0.10% to about 0.4% of tin, by weight of the alloy. A smaller range, in which the tin addition is very effective, is from about 0.1% to about 0.3%. A preferred addition level, within this range, is about 0.2% tin.

To permit a further evaluation of the alloys identified in Table I, electrical conductivities were measured on wires made from these alloys, having a nominal diameter of 0.040 inches, after annealing at 600 C. The conductivities as measured were transformed to percentage values in terms of the conductivity of tin-free alloy No. 1. Since alloy No. 1 has a somewhat higher conductivity than l00% IACS, the conduc tivity values thus determined may be regarded as the lower limits of standard conductivities. These conductivities were plotted in FIG. 2, against the nominal tin content.

The figures readily demonstrate that alloys prepared with additions of tin of0. l or more, up to about 0.4%, are characterized by an increased softening temperature that is commercially attractive. At a tin addition level of 0.2 percent, a very marked increase in softening temperature is obtained that is accompanied by a conductivity that is above 90 percent of the conductivity of the tin-free alloy.

The analytical data presented in Table II is presented to point out the partition of tin between the copper-based matrix and the oxide phases. The chemical analyses for tin was performed by two methods identified as Acid Flux" and HNO dissolution." The first consists of fusing the sample with potassium pyrosulfate and leaching the resulting melt with 10% sulfuric acid. The spectrophotometric procedure which followed is described by E. N. Pollock and L. P. Zopatti, in Analytical Chemistry, 37, 290-1 (1965). The oxygen analyses was performed by the vacuum fusion method with a bath temperature of 1,650" C. HNO; dissolution (column 7 of Table I1) analytical method reports the tin dissolved but does not include the tin combined as an oxide. It is believed that insignificant amounts of tin combined as tin oxide would be dissolved using this analytical technique. The tin content of the oxide and copper phases were also measured on alloys 6, l5, 17, 18 and 19 with the X-ray microprobe using a calibration TABLE I.DATA OBSERVED AFTER THE SECOND ANNEALING Second annealing temperature (1 hr.)

Nominal composition Hardness,

Rockwell F, 572 F. 662 F. 752 F. 812 F. 932 F. 1,022 F. 1,112 F. Softenin Sn, 0 before 300 0. 350 0. 400 0. 450 C. 500 C. 550 C. 600 C. temperature Alloy second No. Percent p.p.m. Percent annealing 16.6% cold worked hardness, Rockwell F C. F.

88% cold worked, Knoop hardness (200 g. load) 15 0. 20 400 0. 04 127. 5 119. 5 110. 5 84. 5 88 73. 5 67 69 ca. 375 ca. 707 17 0. 30 400 0. 04 130. 5 115. 5 90. 5 81 75. 5 79 6S. 5 ca. 375 ca. 707

Exposed to 161 C. for mounting.

TABLE I1.-ANALYT1CAL DATA somewhat higher softening temperature would be anticipated anyway.

Excess Total Free Sn tree Percent Matrix Percent Sn Nommal Sn Percent Sn percent it Analyzed Sn Percent Sn in microcontent Composition Oxygen percent necessary stoichiometric free Sn perpercent Sn as alloy as p b comp analysis, acid to tie up all amount comcent HNO; in alloy SnOe SnOz percent from ave. flux 02 present bined with 02 dissolution (col. 7- (col. 4- (col. 9- Sn electrical percent p.p.m p.p.m. (ave) in alloy (001. 4-c0l. 6) (ave) col. 6) col. 7) col. 4) content rcsistivlty 06 400 236 0660 1484 None 0049 0049 0611 92. 6 Us 05 .10 100 87 .0848 .0371 .0477 .0662 .0185 .0186 21.9 200 156 0996 0742 1254 0511 0257 0485 48. 7 0. 019 10 300 209 0943 1113 None 0198 0198 0745 79. 0 0. 0 .10 400 293 .107 .1484 None .0140 .0140 .0930 86.9 10 400 286 101 1484 None 0170 0170 0840 83. 2 0. 0 11 400 301 113 1484 None 0115 0115 1015 89. 8 0. 025 12 400 303 128 1484 None 0132 0132 1148 89. 7 0. 006 13 400 280 140 1484 None 0137 0137 1263 00. 2 0. 006 15 400 299 153 1484 0046 0254 0208 1276 33. 4 0. 031 14 400 301 160 1484 0116 0381 0265 1219 76. 2 0. 037 200 139 173 i 0742 0988 1125 0137 065 37. 6 0. 069 20 300 268 185 1113 0737 0912 0175 0938 50. 7 0. 106 20 400 231 234 1484 0. 856 1190 0334 1150 49. 1 0. 106 .20 600 296 .159 .2226 None .0817 .0817 0773 48.6 0.094 400 249 282 1484 1336 2155 0819 0665 23. 6 0. 206 .40 400 286 .374 1484 .2256 2940 .0684 .0800 21.4 0. 275 50 400 305 420 1484 2716 358 0864 0620 14. 8 0. 305 0. 368 20 400 17 curve based on a series of oxygen-free copper tin alloys. The TABLE I microprobe analysis (column 11) gives reliable information on a microscopic scale. It is not reliable, however, to determine the average components over a large volume, especially 30 Al 0 if there are fluctuations from point to point. Resistivity meal y N0 20 Wnhout Flrst Anneal surements (column 12) are affected by the dissolved tin only. Condition Average Hardness R7) The sensitivity and accuracy of the resistivity measurements is not very good at low-tin levels. The microprobe analysts and Asswaged 8] the resistivity measurements are employed herein to give support and corroboration to the HNO dissolution data. Annealed l hr m From an analysis of the analytical data it can be seen that 350C. 74 not all ofthe oxygen is tied up as SnO even though there is ad- 400 C 72 ditional free tin in the alloy. This fact cannot be anticipated 425C 71 40 450C. 35 from a study of the literature references referred to above. c 6

To determine whether or not the method of preparing the 600C 3 specimens or the heat treatment was critical in obtaining a copper alloy with a high-softening temperature Alloy No. 20 sofiening ,empemure 44050 was prepared. Alloy No. 20 was prepared containing nommauy 004% (400 oxygen and 9 Alloy (Softening temperature is the interpolated temperature alwhich the hardness is ex- No. 20 was prepared as the specimens previously described pemdm be (Alloys ll9) except a slower cooling rate was used in the casting process. It was anticipated that this change would increase the degree of microsegregation in the casting (i.e., fluc- 50 TABLE [V tuation of alloy contents from spot to spot on a microscopic scale). To the contrary, the microsegregation was markedly decreased. At any rate, the cooling rates used during the Alloy N020 with First Anneal preparation of these specimens were similar to those which would prevail during a commercial manufacturing operation. Annealed 1 hr. at Average Hardness (R,) The cooling rates used during the preparation of the alloys 1 through 19 would be unrealistically fast for a commercial 400C, 68 operation. Analyzed total tin content of Alloy No. 20 was 425C. 67 0.17% tin. 450C 59 Specimens were ground to 0.475 inch diameter, then swaged to 0.373 inch diameter (reduction of area 38 percent). I The heat softening behavior was then tested in this condition Sofiemng empmwm 459 without what was previously called the first anneal (i.e., 1 hour at 600 C. The results are shown in Table III.

In another experiment the as'swaged specimens mentioned Of the specimens described in Table l and Table 11 above, above (0.373 inch diameter) were heat treated for 1 hour at Alloy No. 12 is the closest in composition to Alloy N0. 20. 600 C. (1 15., fir 21 waged o 0.339 in h Alloy No. 12 contained nominally 0.04% oxygen and 0.17% diameter (area reduction of 18 P Softening behavior tin, and analyzed 0.16% tin. Therefore it can be considered was tested f 15 reported In Table 70 similar to Alloy No. 20 except for the cooling rate during cast- The comparison of the results shown in Tables I and 11 ining. Specimen Alloy No. 12 (with the first anneal and after dicate that the softening temperature is somewhat higher with a reduction of area of 16.5 percent) yielded a softening tema first anneal. However the reduction of area prior to second perature of 435 C., which compares with 459 C. (with a first anneal was low (18% as compared to 38%), therefore a anneal) and 440C. (without a first anneal) for Alloy No. 20

reported in Tables [11 and 1V.

From these results it can be deducted that slow cooling dur- .ing casting and the first anneal were found to slightly increase the softening temperature. but neither process can be considered to be critical. Therefore it must be surmised that the method in which the tin is retained in the copper matrix does not appear to depend upon the casting or heat treating procedures.

What I claim is.

1. An oxygen-bearing copper alloy having a softening temperature of at least 400 C. consisting essentially of copper. tin and oxygen. wherein the nominal tin content is therefor. from about 0.2% to about 4%. the nominal oxygen content is from about 0.01% to about 0.06%. and the balance copper.

2. An alloy in accordance with claim I wherein from about 0.10% to about 0.30% ofthe tin is present as free tin.

3. An alloy consisting essentially of copper. tin and oxygen having a softening temperature of at least 400 F.. wherein the total tin analysis is from about 0.15% to about 0.40% the oxygen content is from about 0.01% to about 0.06%. the tin combined with oxygen analysis is from about 0.05% to about 013% and the balance copper. 

2. An alloy in accordance with claim 1 wherein from about 0.10% to about 0.30% of the tin is present as free tin.
 3. An alloy consisting essentially of copper, tin and oxygen having a softening temperature of at least 400* F., wherein the total tin analysis is from about 0.15% to about 0.40% the oxygen content is from about 0.01% to about 0.06%, the tin combined with oxygen analysis is from about 0.05% to about 0.13% and the balance copper. 